The invention is directed to a disconnect and overload bypass arrangement for a hand-held, portable tool which reduces the torque of the electric motor of a portable tool such as an angle grinder, drill or the like during overload situations.
It is known to equip such tools with a safety thermal disconnect switch capable of automatically cutting off the supply of current in the event the electric motor overheats, for instance, as a result of excessive loads applied to the tool by the operator. After the motor cools, the thermal disconnect will automatically reclose thereby permitting resumption of the normal operation of the tool. Thus, thermal disconnect switches temporarily disconnect all electrical energy from the tool motor so that it appears as if the tool is completely deenergized. However, as soon as the motor has cooled, the thermal disconnect will close and again apply energy to the motor.
Everything is in order if the operator is attentive and has the tool under control even during the overheat condition. If, however, as happens frequently, the operator will put the tool down without turning off the on-off switch. Under these circumstances, the tool with restart of its own accord when the thermal disconnect switch cools and recloses. If the tool is improperly set down by the operator, then the tool could move about the work area in an uncontrolled manner causing damage to property and even injury to personnel.
In addition to the above, disconnect switches relying on only thermal action often require a relatively long time to reclose so that the operator of the tool loses time in the performance of his assigned task.